The present invention relates to an improved method of manufacturing gas springs, and more particularly, to an improved method of efficiently and inexpensively manufacturing a gas spring where the gas spring cylinder has an axial, fluid communication channel through which gas (fluid) may be bypassed around or across the gas spring piston assembly and which has a preselected cross-sectional area profile so as to provide the gas spring with predetermined operating characteristics.
Gas springs have been used in many fields, including the automotive field where they have been employed to facilitate and control the movement of hatches, lids and liftgates. Generally speaking, gas springs include, among other components: a cylinder that defines an internal tubular cavity; a piston assembly reciprocally moveable within and dividing the tubular cavity into compression and extension working chambers; a shaft connected and moveable with the piston assembly, with one end of the shaft projecting out of an end of the tubular cavity; and: end caps for closing the ends of the tubular cavity, with one of the end caps also including a seal for the reciprocally moveable shaft as it moves with respect to that end cap.
In normal gas spring operation, the piston assembly, and its projecting shaft, may extend or retract at a nominal rate due to the metering of the gas across the piston assembly. Various structures, including control-flow orifices in the piston assembly and channels or grooves in the inner face of the cylinder, have been utilized in the past to meter or control the passage of gas between the working chambers across the piston assembly as the piston assembly moves within the tubular cavity.
In some applications, the shaft may be decelerated during the extension stroke of the gas spring, and before the shaft is extended fully and stops by including a higher viscosity fluid in the tubular cavity. This fluid causes the piston assembly to slow incrementally and thus provides a xe2x80x9ccushionedxe2x80x9d stop. This higher viscosity fluid, end-of-travel damping technique is, however, orientation sensitive. The gas spring must be in a shaft-down orientation through its extension stroke or else the higher viscosity fluid will meter through the piston assembly prematurely, and the end-of-travel damping feature is lost.
In many automotive environments (for instance, when gas springs are used with hatchbacks), this required shaft-down orientation cannot be maintained. Hence, this end-of-travel damping feature has been unavailable in such xe2x80x9cflip overxe2x80x9d automotive environments without significant component additions that cause the price of the gas springs to be increased significantly.
As noted, channels or grooves have been provided in the inner face of gas spring cylinders to interconnect the gas springs"" two working chambers. U.S. Pat. Nos. 4,643,011 and 4,866,966, issued Feb. 17, 1987, and Sep. 19, 1989, respectively, discloses such axial cylinder channel or grooves. These channels or grooves, are relatively expensive to provide because their manufacture requires specialized, relatively sophisticated tooling and manufacturing operations separate and apart from the manufacture of the cylinder itself.
It is a primary object of the present invention to provide an improved method for manufacturing gas springs where the gas spring cylinder includes an axial, fluid communication channel that interconnects the two working chambers in the gas spring and that serves as a flow path (orifice), between the two working chambers, across or a bypass around the gas spring piston assembly. Preferably, the fluid communication channel initially extends continuously between the ends of the cylinder and includes a uniform, initial cross-sectional area profile. Thereafter, the initial cross-sectional area profile of one or more of the channel portions is selectively changed or varied, relative to the initial profile of the other channel portions, so that the selectively changed cross-sectional area profile(s) will provide the gas spring with desired operating characteristics. The manufacturing method of the present invention is particularly suited for the efficient, relatively inexpensive mass production manufacture of gas spring cylinders, and thus gas springs, using conventional tooling while still permitting customization or selective designing of the gas spring""s operating characteristics for a variety of different applications.
More specifically, a fluid communication channel is preferably initially made in the cylinder at the time that the cylinder itself is made with the entire length of the continuous channel having a uniform or the same, initial cross-sectional area profile. After the cylinder is cut to the desired length for the contemplated gas spring, one or more selected portions of the channel then have their initial, cross-sectional area profile changed. This change in the cross-sectional area profile causes preselected changes in the rates of flow of gas through the channel and bypassed around or across the piston assembly. This results in the gas spring having predetermined, desirable operating characteristics.
The change in the initial cross-sectional area profile of one or more portions of the channel may be accomplished in a variety of ways. Preferably the profile of a channel portion is reduced by applying external force or pressure to the outer face of the cylinder, adjacent to and oriented radially aligned and opposed to the selected channel portion, so as to reduce the profile and thereby restrict, relative to adjacent channel portions, the flow of gas through the changed portion.
In an application, it may be beneficial that the gas spring shaft should come to an intermediate stop (that is, a stop before its normal end-of-stroke stop). The portion of the channel, adjacent to where the piston assembly is to come to such an intermediate stop, will then be changed or xe2x80x9ccrushedxe2x80x9d so as that its cross-sectional profile area is reduced to approaching zero (that is, exhausted) and so that the portion will be left with a smooth, rounded surface, which corresponds with the rest of the inner face of the cylinder.
Similarly, when it is desired that the piston assembly, and thus the gas spring shaft, decelerate before reaching a stop, the cross-sectional area profile in the channel portion, immediately preceding the stop, may be reduced, relative to the cross-sectional area profiles of the channel portion(s) before (or upstream) of the stop. This channel profile change (reduction) proportionally reduces in the velocity of the gas spring""s shaft""s rate of movement through the reduced cross-sectional area profile portion. Hence, the use of the fluid communication channels, made according to the present invention, eliminates the requirement that a gas spring be disposed in a shaft-down orientation to have a desired deceleration of the piston assembly and shaft before stopping.
Another object of the present invention. is to provide an improved, efficient, relatively inexpensive method of manufacturing gas springs of the type described comprising the steps of: making a fluid communication channel in the inner face of the cylinder, where the fluid communication channel has an initial, predetermined cross-sectional area profile, is open to the tubular cavity and extends axially in the inner face so that the fluid communication channel may provide a path for the flow of fluid between the first and second working chambers and for bypassing around or across the piston assembly as the piston assembly reciprocally moves within the tubular cavity; and changing selectively the initial cross-sectional area profile of at least a portion of the fluid communication channel so that the rate of flow of gas or fluid through the fluid communication channel and bypassed around or across the piston assembly, when the piston assembly is adjacent to the channel portion, is selectively changed as compared to the rates of flow of fluid through the fluid communication channel and bypassed around or across the piston assembly when the piston assembly is adjacent to other channel portions that have different cross-sectional area profiles. A related object of the present invention is to provide an improved method, as described, where the fluid communication channel is made as the cylinder is being made; where the fluid communication channel is made so as to extend continuously between the ends of the cylinder; where the initial cross-sectional area profile of the fluid communication channel is substantially the same throughout the fluid communication channel, where the initial cross-sectional area profile of more than one portion of the fluid communication channel is selectively changed; and where channel making means are used to make the fluid communication channel. Another related object of the present invention is to provide an improved method, as described, where changing the initial cross-sectional area profile of the channel portion includes the step of exerting selective forces on the outer face of the cylinder, adjacent to the channel portion, so as to reduce the initial cross-sectional area profile of the channel portion, relative to the initial cross-sectional area profiles of other portions of the fluid communication channel. Still another related object of the present invention is to provide an improved method, as described, where the initial cross-sectional area profile of the channel portion is reduced to approaching zero so that gas or fluid is prevented from flowing through the channel portion and bypassing around or across the piston assembly when the piston assembly is disposed adjacent to the channel portion.
A still further object of the present invention is to provide an improved gas spring manufactured by the improved method as described.
These and other objects, benefits and advantages of the present invention will be more apparent from the following description of the drawings and the preferred embodiments of the present invention.